Sugar cane is a tall growing monocotyledonous crop plant that is cultivated in the tropical and subtropical regions of the world primarily for its ability to store high concentrations of sucrose, or sugar, in the internodes of the stem. Sorghum is a close relative of sugarcane and like sugarcane, particular varieties of sorghum, known as “sweet sorghums”, also accumulate large amounts of sugar in their stems. Near the time of grain maturity, sweet sorghums have 10 to 25% sugar in stalk juice, with sucrose being the predominant disaccharide.
The Australian sugar industry produces raw and refined sugar from sugarcane, with approximately 85% of raw sugar produced in Australia exported, the net income for Australia from sugar sales in 1999/2000 being approximately $1 billion (SRDC 2002).
Traditionally, sugar is initially extracted from the raw cane at sugarcane mills distributed throughout the growing region. Typically, the sugar cane grows for 10 to 18 months before harvest and mature sugar cane stands between two to four metres high and is ideally harvested when the sugar content is at its highest. In Australia and other technically advanced countries, sugar cane is harvested by a variety of mechanical harvesters, which cut the cane stalks off at their base, close to the ground, and feed the cane stalks through a variety of cutting implements to produce billets of cane which can be readily collected and transported to the mills for further processing.
The billets of cane are typically collected in bins and are hauled to the sugar cane mills by a variety of methods, such as diesel locomotives or the like. The cane is typically processed such that the cane harvested earliest is processed first to maintain a fresh cane supply to the mill. The cane is then typically shredded in a hammermill to shred the cane into fibrous material. In this regard, the cells in the cane stalk containing the sugar juice are ruptured but no juice is extracted at this stage.
The shredded cane is then typically fed through a series of crushing mills to extract the sugar rich juice from the fibrous material, and the juice is then pumped away for further processing. The left over fibrous material is called bagasse, which can be used as a fuel source for the mill. It has been found that the efficiency of juice extraction from such crushing or squeezing methods is quite low, and in some cases losses can be as high as 50%. This is typically due to the insufficient cell disruption of the fibrous material and in many instances, full release of the secondary plant substance, which is partly fixed to the cell structure of the fibrous material, is not possible with such traditional mechanical processes.
The juice is then typically heated under pressure in the presence of lime to facilitate precipitation of impurities, such as soil etc present therein, which are removed in a clarifier in which such impurities settle at the bottom thereof as mud. In this regard, the clear or clarified juice is drawn from the top of the clarifier and concentrated to syrup by boiling off the excess water in an evaporator station. The syrup is then made to go through multiple rounds of crystallisation to extract the sucrose after which the product is boiled and the sucrose separates from the remaining molasses fraction. The raw sugar is then cooled and dried and shipped in bulk to sugar refineries worldwide for further purification, resulting in a high quality purified product.
With the traditional systems of harvesting and processing the sugar cane into its various by-products, the sugar cane crop is typically fully harvested and removed from the field resulting in a loss of biomass which must be compensated for by the application of fertilizers and the like to the fields to maintain crop production levels. All the fibre generated during the production process is typically retained at the mill where it is used as fuel to generate electricity for the mill or sold as stockfeed or fertiliser whereby little benefit is gained by the original producer of the cane.
Further, as the sugar cane in the form of billets is transported over significant distances to the mill by a variety of transport methods, transport and handling costs are typically high. As the billets account for a significant volume of raw material, relatively large vehicles are required to transport the cane, creating a further burden on local and governmental infrastructure to support such transport vehicles.
Equally, the milling procedure generates a variety of useful by-products, other than raw sugar. These by-products include ethanol, which can be produced from fermented molasses and used as a fuel, or a cleaning product or in perfumes and bricks; molasses, the final syrup product which can be used as stock feed for cattle as well as a raw material for the production of alcohol and carbon dioxide; and mud and ash, which is the residue left after filtering which can be used as soil conditioners and fertilizers. As the cane grower does not directly have access to these by-products as they only become available through the milling procedure, it is difficult for the grower to market and trade in these goods to provide additional diversification opportunities.
Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.